Redox rates, bismuth-molybdate

Mann and Ko [202] likewise examined the selective oxidation of isobutene on bismuth molybdate. With an integral flow reactor, the highest selectivity was obtained at over 30% conversions for an oxygen/olefin ratio of 2/1 and a W/F = 2.5 g h mol-1 (390°C). The data were correlated with a rather complicated Langmuir—Hinshelwood expression inconsistent with a redox mechanism. This was based on a rate-controlling step between adsorbed isobutene and adsorbed oxygen, and included an inhibiting effect of methacrolein by competitive adsorption with isobutene, viz. 

Ammosov and Sazonov [21,22,24] demonstrated that for iron antimonates the initial selectivities are lower than for bismuth molybdates due to a higher rate of the parallel combustion reaction. It is proved that both selective oxidation and combustion occur by a redox mechanism. In another publication [23], the same authors report the kinetics of the butene and butadiene combustion reactions. 

Although catalytic oxidation of propylene has been found to be first order with respect to the olefin (5), a dependence on oxygen has also been reported (9, 54). Investigations of the participation of lattice oxygen in the oxidation process over mixed oxides, which were thought to contain antimony(V), antimony(III), and tin(IV), reported no support for the redox mechanism observed with bismuth molybdate. The matter of oxygen participation has also been considered by Christie et al. (53), who reported that the rates of... 

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